The present invention relates to photographic film projection systems, such as photographic film slide projectors and motion picture projectors, and more particularly to a system utilizing a plurality of such projectors and which provides for dissolves, laps and other special effects between the various projectors.
At the present time it is known that a plurality of photographic film projectors may be used to present a slide show or motion picture show on a single projection surface such as a screen. For example, two slide projectors may be directed at the same screen and may be timed to present slides alternatively or in some other order. When the first slide projector is "on," i.e., its lamp is lighted, an image on the screen is projected from its slide. The first slide projector may then be turned "off," i.e., its lamp dimmed so that it is effectively extinguished, and a second slide projector, also directed at the same area on the same screen, may be turned on, projecting an image from the photographic film slide in the second projector. The use of a multiplicity of projectors has found especially wide favor in many contexts, including industrial exhibits, multi-media presentations, stage presentations and educational slide film presentations.
It is also known at the present time that the transition from one projector to the other may be made by a control instrument either by means of a manual switch or by means of a program device connected to that control instrument. The transition from one projector to the other may be made slowly so that the light from the first projector gradually fades while the light from the second projector gradually increases. This type of changeover, with its gradual increase and decrease of light, is called in this context a "dissolve" and the control instruments are termed "dissolve instruments," the term used herein, or "dissolvers" or "dissolve modules," although they are generally capable of other control functions in addition to dissolving of images. Prior to such lamp control dissolver instruments it was known to obtain a dissolve in a single projector using an iris diaphragm, as in U.S. Pat. No. 887,839, or a louvre diaphragm, as in U.S. Pat. No. 837,942.
There are a number of such presently commercially available dissolver instruments. In general, the dissolver instruments have two or more multi-terminal connector portions which receive another portion of the connector from two or more slide projectors. In addition, they have manually operated switches (i) determining whether the control is operated manually or from an external program device, (ii) for reversing the image from one projector to another, (iii) a lap control switch, and (iv) a lap dissolve control.
These dissolver instruments, in general, operate quite satisfactorily with projectors using incandescent lamps, for example, the incandescent lamp slide projectors of the types manufactured by Kodak and Bell & Howell. Certain incandescent bulb slide projectors may be modified by insertion of a higher wattage incandescent bulb and there are presently commercially available such modified slide projectors having bulbs to 1200 watts. However, even the larger size bulbs, namely, the 1200 watt bulbs, do not produce a sufficient lumen output in many applications, particularly in use in stage presentations, theaters, or where the presentation is under daylight conditions. In addition, such large incandescent bulbs are very hot and must be cooled, and may last for only 12-20 hours of projection time.
There are also presently commercially available a number of slide projectors which use arc lamps as their light source; for example, a xenon lamp projector is available from Bergen Expo Systems, Inc. of Clifton, N.J. Such arc lamps produce a relatively high level of illumination and provide a relatively long useful life. However, the dissolve instruments presently available cannot be used with arc lamps because they operate by regulating the current to the lamp. When the current to an incandescent bulb is decreased, the bulb becomes decreasingly bright, i.e., the bulb dims in proportion to the decrease in current. However, if current is decreased to an arc lamp such as a xenon bulb, the arc becomes extinguished.
It is not possible, consequently, to dim an arc lamp in proportion to the current regulated by dissolve instruments. The programs prepared by directors are generally prepared on slide projectors using incandescent bulbs which are readily available in many studios. However, those programs, either manual clues or an automatic program, cannot then be utilized with the more powerful arc lamp type of projectors.
There are available a number of special arc lamp projectors which have built-in dissolve and lap controls. It is necessary for the user to evolve an entirely new program for these special arc lamp multiple projectors and to learn to use their special controls. He cannot use the dissolver instruments with which he has become familiar or with which the original program was prepared. One of these types of multiple projector instruments having dissolve controls is Model 5-12, manufactured by Optical Radiation Corp. It is a large instrument, difficult to ship, incorporating two projectors, a complex motor driven mirror system, and a single arc light source. The mirror system shifts the light source from one projector to the other under control of the instrument's internal system. In another double projector system, shown in U.S. Pat. No. 3,358,558, light from either one projector or the other may be blocked by opaque masks which may be positioned in front of the projectors.